A Catalytic Domino Approach toward Oxo-Alkyl Carbonates and Polycarbonates from CO₂, Propargylic Alcohols, and (Mono- and Di-)Alcohols

Abstract

We have explored the domino reaction between propargylic alcohols, carbon dioxide, and various alcohols with the double objective to prepare oxo-alkyl carbonates with a high yield and selectivity under mild conditions and to extend the process to the synthesis of phosgene-free polycarbonates. We first searched for a common catalytic system that was highly selective for the two reactions involved in the domino process, i.e., the cycloaddition of CO2 to propargylic alcohol to yield α-alkylidene cyclic carbonate (αCC) and the alcoholysis of αCC to furnish oxo-alkyl carbonate. Kinetics studies monitored by operando IR spectroscopy and supported by 1H NMR analyses and DFT modeling have permitted us to identify an efficient binary catalytic system composed of a combination of tetrabutylammonium phenolate [TBA][OPh] and silver iodide (AgI) (or copper iodide (CuI)) and to understand its action mode. The [TBA][OPh]/AgI catalytic system (5 mol %) was then successfully implemented for the selective preparation of a range of oxo-alkyl carbonates by the domino reaction with alcohols and propargylic alcohols of different structures. Most of these oxo-alkyl carbonates were produced at a high yield (≥97%) under mild operating conditions, i.e., at 60 °C and 1 bar of CO2. The one-pot synthesis of various poly(β-oxo-carbonate)s from bis(propargylic alcohol)s, diols, and CO2 was finally investigated, and the best operating conditions ([TBA][OPh]/AgI (10 mol %), 60 °C, 15 bar) afforded polycarbonate oligomers with weight-average molar masses of 4300 g/mol. Although the system should be optimized to produce longer polymer chains, this process offers a new phosgene-free alternative to the synthesis of functional polycarbonates poly(β-oxo-carbonate)s) under mild conditions.

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